stupid engine is making rust, now it wont run properly and keeps pumpin gunk into the fuel tank

so i finally decided to take my kyosho gx12 apart. inside as i slowly remove the parts there was heeps of brown liquid everyhwere! inside i saw the main culprit is the ball bearings, thy are creating heeps of rust, after wahing out all the parts with WD-40, the only rust left is the one which has been stained to the walls of the crank case and con-rod.

how can i thoroughly clean the engine ? can i soak the whole crank case in some gasoline ?
what will clean the rust stains

after that how do i put in new bearings ? i know how to remove them.
i'll only put new bearings if my local rc shop has replacement ones

ive been considering replacing my whole engine. but with a different one ofcourse. i wanted to know if any engine within the .12 or .15 engine will fit the kyosho pureten gp alpha ?

or what other engines will fit in there ? hopefully someone can point me to a cheap used one as i am low in cash.

thanx to evry1 who can help

I beleive all the .12/.15 engines have the same mounting dimensions, and all you need to look for is the crankshaft length (Associated uses short crank, but a long one can be cut off for use in Associated cars). Also if you want recoil start or not, as the cars equipped w/ recoil may use taller engine mounts for clearance and a different header pipe. If you change engines, it will be easier if you stay with the same style carb that you have (rotary vs. slide) for ease of hook up. If you disassemble your engine and clean it out, replace bearings, you should be able to use it with no problem. I hate the idea of buying a used engine, as you usually are getting someone elses problems/junk. Keep an eye out for sales on new engines, I see good prices advertised in R/C car action magazine and at Tower (go to their sale section of website). Good luck.

BTW, to avoid more rust in the future, start using an after run oil.